Not applicable.
Not applicable.
This invention relates to an all mechanical support surface which synthesizes the flotation properties of a true fluid. Specifically, this invention relates to a non-pneumatic support surface that has the capability of assuming the shape of the person lying or sitting on it to minimize the force differential on different areas of the skin of such person. This characteristic of the support surface is particularly critical to facilitate blood flow particularly where the user is handicapped, bedridden or disabled.
The present invention provides the flotation properties of a true fluid as follows: (1) Low surface tension caused by providing a highly displaceable support surface. (2) Buoyancy caused by providing suspension forces that have a constant restoring force which is independent of immersion depth. (3) Wetted surface equivalence is provided by shape compliance, where the application of suspension forces at the tissue-surface interface has multiple degrees of freedom to align with and envelope the shape of the person at the contacted surface areas. (4) Low friction to maintain the constant restoring force properties of the moving elements (piston) throughout the immersion depth of the device. (5) Low friction at the tissue interface, using dry lubricant techniques, e.g., teflon-coated fabrics, to permit some sliding as the shape fitting is occurring. (6) Viscosity control with dash-pot techniques, to maintain the feel of a true fluid and to provide slow changes when a floating body moves. Motion control is of great importance when serving the safety needs of the disabled person. High viscosity, however, does not provide positional stability to the supported object. Stability is defined as: when an object moves after receiving a disturbing force it will return to its initial position after the disturbing force is removed.
A support surface having the foregoing characteristics is especially important when used by persons prone to decubitus ulcers which occur when deformation occurs on areas of the body inducing interference with the flow of blood at the contacted site.
One solution to this problem is the use of cellular air filled cushions and the inventor of this application has numerous patents which are directed to air inflatable cushions which have upstanding soft flexible cells, many of which have finned sides, known as ROHO DRY FLOTATION cushions and mattresses. Among these are patent numbers 3605145, 3870450, 4005236, and 4541136, all issued to Robert H. Graebe. These cushions are made from neoprene rubber or plastic films to create a highly displaceable high resolution surface. The cells also are interconnected pneumatically in what are known as xe2x80x9cfeedback pathways.xe2x80x9d The cells in a particular cushion may all be interconnected or sets of said cells can be isolated from other sets in the same cushion with the cells in each set interconnected to allow for positioning of the user in a desired stable position on the cushion. Among patents with such configurations are 5052068, 5163196, and 5461741. These cellular air-filled cushions can be constructed to fit on the mechanical piston of this invention.
In the ROHO cushions, each air cell acts as a piston to develop constant restoring forces as a function of its internal air pressure and because of the feedback pathways they all have the same restoring force to buoy up the person being supported. The use of feedback pathways causes a catastrophic failure mode, when an aircell develops a leak, and the support surface goes flat. By design each air cell has the same effective piston size to assure uniformity of forces across the support surface. Having different sized pistons and therefore non-uniform forces produces a change in wetted surface area and shape compliance but the total summation of all the suspension forces contributing to buoyancy still must equal the weight of the person being supported. Uniform cell (piston) size and/or cell shape facilitates production and inventory issues more than suspension performance results. These air filled cushions or mattresses with slow air flow feedback paths create a high viscosity effect and permit selecting immersion depth for each individual by adjusting the internal working pressure of the cushion.
The soft flexible cells provide multiple (6) degrees of freedom at the tissue interface by deforming to align with the contours of the supported object to enhance its wetting equivalence to a true fluid. The multiple fin design is employed to create gluing surfaces between individual cells and may have some effect on suspension performance which cannot be measured when compared to a more simple non-finned cell.
It is a principal object of the present invention is to provide a mechanical device which emulates the effect of the aforementioned ROHO air cell cushions and mattresses. Another object is to provide a cushion and mattress constructed from rigid materials which still will provide the flotation properties of a true fluid. Still another object is to provide a cushion and mattress which has a series of reciprocal piston heads which are controlled by constant restoring force springs whereby the force exerted by the piston head is constant regardless of its travel within its movement limits.
A further object of this invention is to provide a cellular cushion and mattress construction in which the cells (pistons) are mechanical and are easily replaceable to adjust the restoring force of the cells to accommodate users of various body weights and contact areas. A further object is to provide a means to dampen piston movement rates to create viscosity control. A further object is to provide a support surface that does not have a catastrophic failure mode.
Still another object is to provide a mechanical cushioned mattress using reciprocal piston rods operated by constant restoring force springs which can be located inside or outside the piston to change the surface area and density of the pistons. Another object is to provide mechanical piston operated cushions and mattress in which the end of the piston rod has multiple degrees of freedom. These and other objects and advantages will become apparent hereinafter.
The present invention comprises mechanically operated mattresses and cushions which are controlled by constant restoring force springs and the arrangements and combination of parts simulate the flotation properties of a true fluid.